For reference, what carb is on it? I can give you the general idea without knowing what carb it is. It may have a fixed jet Hi speed bypass or it may not. The only way I know to service the metering lever is to remove the metering cover, gasket and diaphram (not necessarily in that order). Then, there should be the metering lever, a spring under the metering lever, a bar it pivots on and a screw holding down the bar. Remove the screw and you should be able to pull the metering lever out, the needle should come out with it. Careful of that spring! I would replace the needle from a carb rebuild kit from your local Stihler ship. In fact, why not rebuild the whole carb while you are at it, especially if you use ethanol gas. Spray the seat out with carb cleaner, while the needle is out.
